The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.
The present invention relates to the field of permanent magnet structures and, more particularly, to apparatus and method for making permanent magnet toroid rings.
Permanent magnet structures that produce a working magnetic field are well known in the art. The term xe2x80x9cworking magnetic fieldxe2x80x9d as used herein refers to a magnetic field that is used to do some type of work. A magnetic field used to magnetize unmagnetized material (e.g. permanent magnet material) is an example of such a working magnetic field.
Some permanent magnet structures are composed of pieces of permanent magnet material arranged to form a shell having an interior cavity wherein the working field is generated. Each piece of permanent magnet material has a magnetization that adds to the overall magnetization of the shell. Depending on the overall magnetization of its shell, a permanent magnet structure can be designed to generate a working field having a given magnitude and a given direction within its cavity.
As stated above, such working fields have been used to magnetize unmagnetized permanent magnet material. Basically, the unmagnetized material is placed in the cavity in which the working field is generated. The working field, depending on its strength and direction, thereby magnetizes the unmagnetized material.
One type of permanent magnet structure used to magnetize permanent magnet material is disclosed in U.S. Pat. No. 4,911,627, entitled xe2x80x9cApparatus For Fabrication Of Permanent Magnet Toroidal Ringsxe2x80x9d, issued to the present inventor on Mar. 27, 1990, and incorporated herein by reference. As taught therein, a hollow cylindrical flux source, formed into a toroidal shape, can be used to magnetize a solid toroidal ring made of unmagnetized material. The hollow cylindrical flux source is basically a shell of permanent magnet material having a cylindrical cavity in which a working field is generated. To become magnetized, the solid toroidal ring is placed in the hollow cylindrical flux source""s cavity such that it is exposed to the working field therein. The working field thereby magnetizes the solid toroidal ring. The magnetization of the solid toroidal ring depends on the direction and strength of the working field. The hollow cylindrical flux source can be thought of as a fixture in which the solid toroidal ring is magnetized.
The problem with the ""627 method, however, is that the magnetization fixture (i.e. the hollow cylindrical flux source) can only produce a magnetized toroidal ring having a unidirectional magnetization. That is, the magnetization of the toroidal ring is in the same direction at every point along the ring""s azimuthal axis. This is due to the fact that the hollow cylindrical flux source, or fixture, taught in ""627 has a working field that is unidirectional along its azimuthal axis. Such a unidirectionally magnetized solid toroidal ring may not be desirable for all applications.
The present invention is a method and apparatus for fabricating solid toroidal rings such that they have a magnetization that changes or alternates direction along their azimuthal axis.
In accordance with the principles of the present invention, a toroidal ring having such an alternating magnetization can be made by first placing an unmagnetized solid toroidal ring , usually of square of rectangular shape, into a first magnetization fixture. The first magnetization fixture is operable to magnetize only given regions or points of the solid toroidal ring. The result is a first-magnetized ring that has a magnetization with a first direction in only the given regions of the ring. The other regions remain substantially unmagnetized or weakly magnetized. The first-magnetized ring is then placed into a second magnetization fixture. The second magnetization fixture is operable to only magnetize the unmagnetized or weakly magnetized regions of the first magnetized ring such that the unmagnetized regions become magnetized in a direction that is opposite to the first direction. The result, in accordance with the principles of the present invention, is a solid toroidal ring having a magnetization that completely reverses direction at given points along its azimuthal axis.
In particular embodiments, each magnetization fixture is a hollow cylindrical flux source that is equatorially split into two halves. When the two halves are brought together they form a hollow cylindrical cavity of circular cross-section in which a working magnetic field is generated. Each fixture has a notched filler placed in its hollow toroidal cavity. The notched filler is composed of a passive material such as iron. The notched filler works in conjunction with the hollow cylindrical flux source generate a circumferentially or azimuthally periodic radial working field in the cavity of the fixture. The working field is called a circumferentially or azimuthally periodic working field because it-periodically alternates between a xe2x80x9chighxe2x80x9d and xe2x80x9clowxe2x80x9d level of field strength along the axis of the shell. The field strength is referred to as xe2x80x9chighxe2x80x9d between the iron teeth of the notched filler because the working field in that space of the cavity has a strength that can strongly magnetize (e.g. saturate) unmagnetized material placed therein. The field strength is referred to as xe2x80x9clowxe2x80x9d between the notches of the notched filler because the working field in that space of the cavity has a strength that can, at best, weakly-magnetize unmagnetized material placed therein. The difference between the two fixtures, however, is that notches of the notched filler in one fixture are in the same location as the teeth of the notched filler in the other fixture. As a result, the direction of the circumferentially periodic working field in one shell is opposite to the direction of the circumferentially periodic working field in the other shell. That is, the location having a high field in one fixture will have a low field in the other fixture. Thus, in accordance with the principles of the present invention, successively placing a solid toroidal ring in the two fixtures will result in a magnetized toroidal ring having a magnetization that alternates direction along its azimuthal axis.
These and other features of the invention will become more apparent from the Detailed Description when taken with the drawing(s). The scope of the invention, however, is limited only by the claims.